Structure of the low-temperature phase of Rb3D(SeO4)2 by single-crystal neutron diffraction Original Research Article

Crystal structure of Rb3D(SeO4)2 has been investigated at 25 K (below the transition temperature Tc=95.4 K) by single-crystal neutron diffraction. Accompanying the transition, the SeO4 groups, which are all equivalent in the phase above the transition (space group A2/a), split into eight nonequivalent groups in a superlattice (a×2b×2c, space group A2) in the low-temperature phase. Based on the D atom positions obtained, each of the SeO4 groups was identified to be in the state closer to a HSeO4− ion or to a SeO42− ion and the dipole arrangement of SeO4–D–SeO4 dimer was revealed. This dipole arrangement has ‘ferri’ structure along the polar b-axis, but ‘antiferro’ structure in the plane perpendicular to the b-axis. These results are consistent with the characteristics found in the earlier dielectric measurements.